"PlayStation 4 won't impose any new restrictions on used games. This is a good thing," said Tretton, to huge applause from the audience in attendance. "When a gamer buys a PS4 disc, they have the rights to that copy of the game."

This is completely unenforceable. If people want to sell a game they're done with, they should be able to, or at least trade for another title of equal value. All Sony has accomplished with this draconian rule is guarantee the creation of a thriving underground black market of illegally sold and traded games. Hackers have already proved themselves quite capable of easily bypassing most any means of trying to prevent that.

It USED to be unenforceable. It's very enforceable now. Lets not forget the time they killed the "Other OS" in the PS3 with a simple online SW upgrade. But conceivably, a mandatory account can be enforced on the PSN or even on their own network via the game designer. DRM/Activation is extremely enforceable with today's internet ready consoles albeit not exactly via Sony themselves, but the hardware and firmware is their at their disposal. If it wasn't an option, it simply wouldn't be internet ready.